1. Technical Field
The present invention relates generally to a fuel injection system for internal combustion engines, and particularly to a common rail fuel injection system for diesel engines which may be employed in automotive vehicles.
2. Background Art
The common rail fuel injection system is mostly employed with diesel internal combustion engines for automotive vehicles. Specifically, the common rail fuel injection system is equipped with a high-pressure pump, a common rail, and fuel injectors. The high-pressure pump works to pressurize fuel, as fed from a fuel tank, and supplies it to the common rail. The common rail stores the fuel at a controlled pressure. The fuel injectors spray the fuel, as supplied from the common rail, into cylinders of the engine.
The common rail fuel injection system works to control the flow rate of fuel discharged from the high-pressure pump so as to bring the pressure of fuel in the common rail into agreement with a target pressure in a feedback mode using, for example, a proportional-integral-derivative (PID) algorithm. For example, Japanese Patent First Publication No. 2010-190147 discloses such pump discharge control. The target pressure is usually determined based on operating conditions of the engine such as a degree of load on and speed of the engine. The pressure in the common rail is detected using a pressure sensor.
The fuel injection system, as taught in the above publication, starts to control the operation of the high-pressure pump after a deviation of the pressure in the common rail from the target pressure occurs and, thus, faces a difficulty in controlling the high-pressure pump precisely and quickly in response to the pressure deviation. This may result in a high probability that when the target pressure changes with a change in operating condition of the engine, the actual pressure in the common rail overshoots the new target pressure or hunts around it.